SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
In autobauding mode, the UART can extract transfer characteristics (speed, length, and parity) from an "at" (AT) command (ASCII code). These characteristics are used to receive data after an AT and to send data.
The following AT commands are valid:
AT | DATA | <CR> |
at | DATA | <CR> |
A/ | ||
a/ |
A line break during the acquisition of the sequence AT is not recognized, and an echo function is not implemented in hardware.
A/ and a/ are not used to extract characteristics, but they must be recognized because of their special meaning. A/ or a/ is used to instruct the software to repeat the last received AT command; therefore, an a/ always follows an AT, and transfer characteristics are not expected to change between an AT and an a/.
When a valid AT is received, AT and all subsequent data, including the final <CR> (0x0D), are saved to the RX FIFO. The autobaud state-machine waits for the next valid AT command. If an a/ (A/) is received, the a/ (A/) is saved in the RX FIFO and the state-machine waits for the next valid AT command.
On the first successful detection of the baud rate, the UART activates an interrupt to signify that the AT (upper or lower case) sequence is detected. The UART_UASR register reflects the correct settings for the baud rate detected. Interrupt activity can continue in this fashion when a subsequent character is received. Therefore, it is recommended that the software enable the RHR interrupt when using the autobaud mode.
The following settings are detected in autobaud mode with a module clock of 48 MHz:
The combination of 7-bit character plus space parity is not supported.
Autobauding mode is selected when the UART_MDR1[2-0] MODE_SELECT bit field is set to 0x2. In UART autobauding mode, UART_DLL, UART_DLH, and UART_LCR[5-0] bit field settings are not used; instead, the UART_UASR register is updated with the configuration detected by the autobauding logic.
UASR Autobauding Status Register Use
This register is used to set up transmission according to the characteristics of the previous reception instead of the UART_LCR, UART_DLL, and UART_DLH registers when the UART is in autobauding mode.
To reset the autobauding hardware (to start a new AT detection) or to set the UART in standard mode (no autobaud), the UART_MDR1[2-0] MODE_SELECT bit field must be set to reset state (0x7) and then to the UART in autobauding mode (0x2) or to the UART in standard mode (0x0).
Use limitation: